Constantine II AE follis, Siscia.

CONSTANTINVS IVN NOB C, laureate head right.
CAESARVM NOSTRORVM around VOT X within wreath.
Mintmark BSIS star.

RIC VII Siscia 166, rated R4.

With permission of Roma Numismatics, April, 2011

Known officinae for this issue, with rarity ratings:
BSIS star and epsilon SIS star = R4.
gamma SIS star and delta SIS star = R5